Powder comprising polymer-coated inorganic particles

ABSTRACT

Composite particles comprising core particles completely or partially coated with a precipitated polymer, where the d 50  median diameter of the core particles is from 1 to 70 μm and wherein the core particle is an inorganic material which does not include titanium dioxide are provided. A method to prepare the particles includes dissolution of a polymer in a solvent and precipitation of the polymer in the presence of a suspension of the core particles. Further provided is a layer by layer moulding process employing the composite particles and mouldings obtained therefrom.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Application No. DE102011078722.4, filed Jul. 6, 2011, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a powder based on polymer-coated fillers whichhas advantages in terms of the stability of the production process, anddensity, to the use of the said powder in shaping processes, and also tomouldings produced by a layer-by-layer process by which regions of apowder layer are selectively melted, with use of the said powder. Aftercooling and solidification of the regions previously meltedlayer-by-layer, the moulding can be removed from the powder bed. Themouldings according to the invention moreover exhibit lesssusceptibility to warpage than conventional mouldings.

2. Description of the Related Art

A task frequently encountered in very recent times is the rapidprovision of prototypes. Particularly suitable processes are those whichare based on pulverulent materials and in which the desired structuresare produced layer-by-layer through selective melting andsolidification. Supportive structures for overhangs and undercuts can beomitted here, because the powder bed surrounding the molten regionsprovides sufficient support. Nor is there any need for the subsequentoperation of removing supports. The processes are also suitable forproducing short runs.

The selectivity of the layer-by-layer process here can be provided byway of example by applying susceptors, absorbers, or inhibitors, or bymasks, or by way of focussed introduction of energy, for example througha laser beam, or by way of glass fibres. The energy is introduced by wayof electromagnetic radiation.

A process which has particularly good suitability for the purpose ofrapid prototyping is selective laser sintering. In this process,plastics powders are briefly irradiated selectively in a chamber by alaser beam, and the powder particles which encounter the laser beamtherefore melt. The molten particles coalesce and rapidly resolidify togive a solid mass. This process can provide simple and rapid productionof three-dimensional products by repeated irradiation of a succession offreshly applied layers.

The laser sintering (rapid prototyping) process for producing mouldingsfrom pulverulent polymers is described in detail in the U.S. Pat. No.6,136,948 and WO 96/06881. A wide variety of polymers and copolymers isclaimed for the said application, examples being polyacetate,polypropylene, polyethylene, ionomers and polyamide.

Other processes with good suitability are the selective inhibitionbonding (SIB) processes described in WO 01/38061, and a processdescribed in EP 1 015 214. Both processes operate withlarge-surface-area infrared heating for melting of the powder. Theselectivity of the melting process is achieved in the first case byapplying an inhibitor, and in the second process it is achieved by amask. DE 103 11 438 describes another process. In this, the energyrequired for the fusion process is introduced through a microwavegenerator, and the selectivity is achieved by applying a susceptor.

Other suitable processes are those operating with an absorber which iseither present in the powder or is applied by ink-jet processes, asdescribed in DE 10 2004 012 682.8, DE 10 2004 012 683.6 and DE 10 2004020 452.7.

The rapid prototyping or rapid manufacturing processes mentioned (RP orRM processes) can use pulverulent substrates, in particular polymers,preferably selected from polyesters, polyvinyl chloride, polyacetal,polypropylene, polyethylene, polystyrene, polycarbonate,poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate (PMMA),ionomer, polyamide, or a mixture thereof.

WO 95/11006 describes a polymer powder which is suitable for the lasersintering process and which, when melting behaviour is determined bydifferential scanning calorimetry with a scanning rate of from 10 to 20°C./min, exhibits no overlap of the melting and recrystallization peak,has a degree of crystallinity of from 10 to 90%, likewise determined byDSC, has a number-average molecular weight Mn of from 30 000 to 500 000,and has a Mw/Mn quotient in the range from 1 to 5.

DE 197 47 309 describes the use of a nylon-12 powder which has increasedmelting point and increased enthalpy of fusion and which is obtained byreprecipitation of a polyamide previously produced through ring-openingand subsequent polycondensation of laurolactam. This is a nylon-12.

DE 10 2004 003 485 describes the use of particles with at least onecavity for use in processes that build layers. All of the particlescomprise at least one cavity, and the particles comprising the cavityare melted by introduction of electromagnetic energy. The powderparticles described have a thin surface layer.

DE 102 27 224 describes a granulated material which is intended for 3Dbinder printing and which is composed of particles provided with asurface layer comprising a non-polar external area. The surface layer ofthe powder particles described is, however, thin.

In conventionally known methods, powders such as described above aresometimes mixed with other particles for reinforcement, e.g. metalparticles, glass particles or TiO₂ particles. However, a disadvantageencountered in these processes is that the handling of powder mixturesof this type often leads to demixing phenomena, and the mechanicalproperties that the reinforcing material is intended to achievetherefore sometimes vary. The regions where the proportion of filler istoo high become very brittle and therefore unusable, and the regionscomprising too little filler are softer than intended. The demixingderives from the different density of the polymer particles and of thefiller, and tends to be apparent to some extent during any transport ofthe powder mixture and during its handling. In particular if thehandling of the powder is automated in the rapid manufacturing process,it is difficult to control deviations in the properties of thecomponents produced.

WO 2007/051691 describes processes for producing ultra-fine powdersbased on polyamides, by precipitating polyamides in the presence ofinorganic particles, where a suspension is used with inorganic particlessuspended in the alcoholic medium, where the d₅₀ median size of theinorganic particles is in the range from 0.001 to 0.8 μm. Fine polyamidepowders were obtained here, and, because of their small size, theinorganic particles have uniform distribution in the composite particleshere. The process was aimed at achieving colouring of the powder and ofthe moulding formed therefrom. The measure does not alter the mechanicalproperties of the moulding.

It was an object of the present invention to eliminate the problem ofthe demixing phenomenon and to achieve an improvement in the consistencyof mechanical properties in the moulding, preferably strengthening ofthe moulding, and providing flame retardancy and/or an improvement inthermal conductivity in the moulding, where these improvements areintended to be achieved with the reinforcing material.

SUMMARY OF THE INVENTION

These and other objects have been achieved by the present invention, thefirst embodiment of which includes a powder, comprising compositeparticles:

wherein the composite particles, comprise:

an inorganic core particle having a d₅₀ median diameter of from 1 to 70μm; and

-   -   at least a partial coating of a polymer on the core;

wherein the inorganic core particle material does not include titaniumdioxide, and a melting point of the coating polymer is obtainable whenthe polymer is exposed to an electromagnetic energy.

In a first preferred embodiment, the inorganic core particle of thecomposite particle is at least one material selected from the groupconsisting of silicon dioxide, a polyphosphate, a phosphinate, boroncarbide, a mixed oxide, a spinel and a ceramic In a second preferredembodiment, the polymer of the coating of the composite particlecomprises at least one polymer selected from the group consisting of apolyolefin, a polyethylene, a polypropylene, a polyvinyl chloride, apolyacetal, a polystyrene, a polyimide, a polysulphone, apoly(N-methylmethacrylimide) (PMMI), a polymethyl methacrylate (PMMA), apolyvinylidene fluoride (PVDF), an ionomer, a polyether ketone, apolyaryl ether ketone, a polyamide, and a copolyamide.

In another embodiment a d₅₀ median diameter of the composite particlesis from 20 to 150 μm.

In a highly preferred embodiment, a ratio of a d₅₀ median diameter ofthe composite particles to a d₅₀ median diameter of the core particlesis from 1.15 to 30.

In a further embodiment, the invention includes a process for producingthe composite particles, the process comprising:

at least partially dissolving a polymer for the coating in a mediumcomprising a solvent which at least partially dissolves the polymer;

adding the inorganic core particles to the medium, before, during orafter at least partially dissolving the polymer;

suspending the core particles in the medium; and then

precipitating the polymer from the at least partial solution onto thecore particles to obtain the composite particles; wherein the d₅₀ mediandiameter of the core particles is from 1 to 70 μm.

In another embodiment, the invention includes a process for producing amoulded article, the process comprising:

applying a layer of the composite powder according to the presentinvention;

selectively melting at least one region of the layer by introduction ofelectromagnetic energy;

allowing the melted region to solidify;

applying another layer of composite powder and repeating the melting andsolidification to perform a layer-by-layer process in which a moldinghaving a structure according to the selective treatment is obtained;

wherein the melting selectivity is achieved by applying susceptors,inhibitors, or absorbers to each applied layer or by applying a mask tothe applied layer.

Throughout the following description of the invention numerical rangesand values provided include all values and subvalues therebetween aswell as all intermediate ranges within the stated range values.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One technical object of the invention may be achieved by provision of apowder for use in a layer-by-layer process for producing mouldings byselectively melting regions of the respective powder layer throughintroduction of electromagnetic energy, comprising composite particleswhich comprise an inorganic core particle having a d₅₀ median diameterof from 1 to 70 μm; and at least a partial coating of a polymer on thecore; wherein the inorganic core particle material is at least oneselected from the group consisting of silicon dioxide, a polyphosphate,a phosphinate, boron carbonate, a mixed oxide, a spinel and a ceramic,and a melting point of the coating polymer is obtainable when thepolymer is exposed to an electromagnetic energy.

The core particles are inorganic core particles, with the exception oftitanium dioxide, and where the d₅₀ median diameter of the inorganiccore particles is from 1 to 70 μm. The d₅₀ median diameter of the coreparticles in all three spatial directions here is from 1 to 70 μm. Thedimensions in each spatial direction may be different. It may bepreferable that the d₅₀ median diameter of the core particles in allthree spatial directions independently of one another is from 1 to 70μm. The data for the diameters of the core particles is based on theparticles which provide the core in the composite particle to be formed.

The layer-by-layer process for producing mouldings is preferablyselective laser sintering.

Because of the firm bond between polymer and filler, the powderaccording to the present invention is no longer subject to the problemsof demixing, and this leads to an improvement in consistency ofmechanical properties in the moulding produced from the powder. Sincedemixing no longer occurs in the powder according to the invention, itmay be possible to use the powder according to the invention inconstruction processes to produce uniform components and components withuniform quality. The durably uniform constitution resulting from thefirm bond between polymer and core particle significantly improves therecyclability of the powder, even when a plurality of stages areinvolved. There may also be advantages in the use of the powdersaccording to the invention: the powders according to the invention maybe stored, transported and used in larger packaging units without anypossibility of demixing. Feed quantities of the product may thereforealso be greater during the laser sintering process, i.e. more powder canbe charged to the sample feed container, and/or the dimensions of thesample feed container can be greater, without any resultant adverseeffect on the quality of the resultant components. Furthermore,fluidization in the feed does not lead to the demixing that isrelatively frequently observed in conventionally known systems. Becausethe powders of the present invention have an exterior shell made ofpolymer, the introduction of energy by the laser may also be moreuniform. In conventional powders as described above, the laser sometimesencounters a polymer particle and sometimes encounters a fillerparticle. As a function of filler type, the result can vary in extremecases from almost complete absorption to almost complete reflection ofthe energy. Powders according to the present invention advantageouslyavoid these problems.

Surprisingly, it has now been found that, by using core particles madeof an inorganic material with d₅₀ median diameter of greater than 1 to70 μm as reinforcing material firmly bonded to the polymer (compositeparticles), it may be possible, through a layer-by-layer process (inwhich regions of the respective powder layer are selectively melted) toproduce mouldings which have advantages in relation to density andsusceptibility to warpage and with this have better properties inrelation to consistency of processing than those made of theconventionally known reinforced polymer powders. According to preferredembodiments of the invention reinforced mouldings having improvedthermal conductivity, and/or improved flame retardancy may be obtained.

In one preferred embodiment, the inorganic core particles to be coatedwith the precipitatable polymer may be selected from the groupconsisting of silicon dioxide, polyphosphates, phosphinates, metalnitrides, semimetal nitrides, aluminium nitrides, boron nitride, boroncarbide, metal oxides, for example Al₂O₃, mixed oxides, spinets, metal,ceramic and mixtures thereof. It may be further preferable that the coreparticles to be coated with the precipitatable polymer have beenselected from the group of silicon dioxide, polyphosphates,phosphinates, boron carbide, metal oxides, for example Al₂O₃, mixedoxides, spinels and mixtures thereof. It is moreover possible thatfurther fillers or filler mixtures are present alongside the coreparticles mentioned in the composite particle.

The respective core particles may be of spherical, lamellar or elongateform. The respective core particles may moreover be sharp-edged, roundedor smooth. The core particles mentioned may optionally be coated withsizes prior to application of the polymer coating.

The core particles provide the core in the composite particle. Thepowder according to the present invention preferably has a core-shellstructure.

In another preferred embodiment, the average thickness of the coatingmade of the precipitated polymer may be 1.5 μm or more, preferably 2, 3,5, 10, 15, 20, 25, 30, 50, or 75 μm or more.

In another preferred embodiment, the d₅₀ median diameter of the coreparticles (core of the composite particle) may be from 1 to 60 μm,preferably from 1 to 50 μm, with preference from 1 to 40 μm, morepreferably from 1 to 30 μm, still more preferably from 1 to 25 μm,particularly preferably from 1 to 20 μm and very particularly preferablyfrom 1 to 10 μm. Suitable particle size distributions can be ensured byknown methods, e.g. sieving or sifting.

In an alternative embodiment, the d₅₀ median diameter of the coreparticles (core of the composite particle) may be from 10 to 60 μm,preferably from 10 to 50 μm, with preference from 10 to 40 μm, morepreferably from 10 to 30 μm, still more preferably from 10 to 25 μm andparticularly preferably from 10 to 20 μm. Again in this preferredembodiment, the core particles to be coated with the precipitatablepolymer have been selected from the group of silicon dioxide,polyphosphates, phosphinates, aluminium nitride, boron nitride, boroncarbide, metal oxides, e.g. Al₂O₃, mixed oxides, spinels, metal andceramic and mixtures thereof.

It is moreover preferable that the d₅₀ median diameter of the compositeparticles may be from 20 to 150 μm, with preference from 20 to 120 μm,preferably from 20 to 100 μm, more preferably from 25 to 80 μm andparticularly preferably from 25 to 70 μm.

The ratio of the d₅₀ median diameter of the composite particles to thed₅₀ median diameter of the core particles may preferably be from 1.15 to30, with preference from 1.2 to 30, more preferably from 1.5 to 25;still more preferably from 1.5 to 15, particularly preferably from 1.5to 12 and very particularly preferably from 1.5 to 10.

The ratio by weight of the polymer to the core particles, based on theentirety of the composite particles, is preferably from 0.1 to 30, withpreference from 1.0 to 20.0 and more preferably from 1.3 to 10.0.

In another preferred embodiment, the BET specific surface area of thepowder according to the invention may be in the range from 1 to 60 m²/g,with preference from 3 to 50 m²/g, more preferably from 3 to 40 m²/g;particularly preferably from 3 to 30 m²/g, still more preferably from 3to 20 m²/g and very particularly preferably from 3 to 12 m²/g. The bulkdensity (BD) of the powder according to the invention may be in therange from 120 to 700 g/l, with preference from 250 to 450 g/l.

The precipitated or precipitatable polymer is a polymer which can bedissolved in a liquid medium comprising a solvent and which precipitatesin the form of a completely or partially insoluble deposit in the formof flakes or droplets, or in crystalline form, as a result of changes ofcertain parameters, e.g. temperature, pressure, solvent content,non-solvents, anti-solvents, or precipitants. The type of solvent andthe solvent content depend on the properties of the polymer, as also dothe other parameters for dissolving or precipitating the polymer.

The precipitatable polymer may preferably be selected from polyolefins,polyethylene, polypropylene, polyvinyl chloride, polyacetal,polystyrene, polyimides, polysulphones, poly(N-methylmethacrylimides)(PMMI), polymethyl methacrylate (PMMA), polyvinylidene fluorides (PVDF),ionomer, polyether ketones, polyaryl ether ketones, polyamide,copolyamide and mixtures thereof, in particular mixtures of homo- andcopolyamide.

In another embodiment, the precipitatable polymer for coating the coreparticles may be obtained through precipitation of at least onepolyamide of the AABB type or through joint precipitation of at leastone polyamide of the AB type and at least one polyamide of the AABBtype. Preference may be given here to co-precipitated polyamides, whereat least nylon-11 or nylon-12 and at least one polyamide based onPA1010, PA1012, PA1212 or PA1013 is present.

The following precipitatable polymer and solvent combinations may bementioned as examples. Polyolefins and polyethylene may be dissolved,for example in toluene, xylene and/or 1,2,4-trichlorobenzene.Polypropylene may be dissolved in toluene and/or xylene. Polyvinylchloride may be dissolved in acetone. Polyacetal may be dissolved inDMF, DMAc and/or NMP. Polystyrene may be dissolved in toluene.Polyimides may be dissolved in NMP. Polysulphones may be dissolved insulpholane. Poly(N-methylmethacrylimides) (PMMI) may be dissolved inDMAc and/or NMP. Polymethyl methacrylate (PMMA) may be dissolved inacetone. Polyvinylidene fluorides may be dissolved inN-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide(DMAc) and/or cyclohexanone. Polyether ketones and polyaryl etherketones may be dissolved in diphenyl sulphone and/or in sulpholane.Polyamides may be dissolved in an alcoholic medium, preferably anethanol-water mixture. As explained above, it may sometimes alsonecessary to adjust parameters such as temperature and pressure in orderto dissolve a given polymer.

Once the relevant polymer has been dissolved, the dissolved polymer isprecipitated in the presence of the core particles, in order to coat thecore particles completely or partially with the relevant precipitatedpolymer. The precipitation of the polymer may be initiated and/oraccelerated by changing the pressure, changing the temperature, changing(reducing) the concentration of the solvent, and optionally adding anon-solvent, anti-solvent and/or precipitant. In the case of amorphouspolymers, such as polystyrene, sulphones, PMMI, PMMA, and ionomer, itmay be necessary to add a non-solvent to precipitate the relevantpolymer.

The precipitatable polymer may preferably be a polyamide which has atleast 8 carbon atoms per carbonamide group. The polymer may particularlypreferably be a polyamide which has 10 or more carbon atoms percarbonamide group. The polymer may very particularly preferably be apolyamide selected from nylon-6,12 (PA 612), nylon-11 (PA 11) andnylon-12 (PA 12). The production process for the polyamides that can beused in the sinter powders according to the invention is well-known and,for the production of PA 12, can be found for example, in the documentsDE 29 06 647, DE 35 10 687, DE 35 10 691 and DE 44 21 454. Thegranulated polyamide material required may be purchased from variousproducers, for example, granulated nylon-12 material is available withtrade name VESTAMID from Evonik Industries AG.

In a highly preferred embodiment according to the invention the coatingpolymer is nylon-12.

It may be moreover possible to use the corresponding copolyamides ormixtures of homo- and copolyamides which comprise at least 70 percent byweight of the units mentioned. Accordingly, they may comprise, ascomonomers, from 0 to 30 percent by weight of one or more comonomers,such as caprolactam, hexamethylenediamine, 2-methyl-1,5-pentanediamine,1,8-octamethylenediamine, dodecamethylenediamine, isophoronediamine,trimethylhexamethylenediamine, adipic acid, suberic acid, azeleic acid,sebacic acid, dodecanedioic acid, aminoundecanoic acid. The homo- andcopolyamides mentioned, termed polyamides hereinafter, may be used inthe form of granulated materials or ground material, where the relativesolution viscosity of these is from 1.5 to 2.0 (measured in 0.5%m-cresol solution at 25° C. in accordance with DIN 53 727), preferablyfrom 1.70 to 1.95. They may be produced by conventionally known methods,including polycondensation, or hydrolytic or acidolytic or activatedanionic polymerization. It may be preferable to use unregulatedpolyamides having NH₂/COOH end group ratios of from 40/60 to 60/40.However, it may also be advantageous to use regulated polyamides andspecifically preferably those in which the NH₂/COOH end group ratio is90:10 and 80:20 or 10:90 and 20:80.

In another preferred embodiment, the density of the core particles isgreater than the density of the solvent or not more than 20%, withpreference not more than 15%, more preferably not more than 10% andparticularly preferably not more than 5% less than the density of thesolvent used for the precipitation of the polymer.

It may be particularly preferable to use an alkanol (for example:methanol, ethanol, propanol or butanol), preferably ethanol, as solventfor the precipitation of the polymer in the presence of the coreparticles, where the density of the core particles is greater than thedensity of the alkanol or not more than 20%, with preference not morethan 15%, more preferably not more than 10% and particularly preferablynot more than 5% less than the density of the alkanol, preferably ofethanol.

The powder may comprise the composite particles mentioned alone ortogether with, admixed therewith in uncompacted form, (dry-blend)fillers, and/or auxiliaries. The proportion of the composite particlesin the powder may be at least 50% by weight, with preference at least80% by weight, preferably at least 90% by weight, particularlypreferably at least 95% by weight and very particularly preferably atleast 99% by weight.

The powders according to the invention may optionally compriseauxiliaries and/or other organic or inorganic pigments. Theseauxiliaries may be a powder-flow aid, e.g. precipitated and/or fumedsilicas. Precipitated silicas are available by way of example withproduct name AEROSIL® with various specifications from Evonik IndustriesAG. It may be preferable that the powder according to the inventioncomprises less than 3% by weight of these auxiliaries, with preferencefrom 0.001 to 2% by weight and very particularly preferably from 0.025to 1% by weight, based on the entirety of the polymers present.

In order to improve processability or for further modification of thepowder according to the invention, inorganic foreign pigments, e.g.transition metal oxides, stabilizers, e.g. phenols, in particularsterically hindered phenols, flow aids and powder-flow aids, e.g. fumedsilicas, may be added. The amount of the substances added to thepolymers, based on the total weight of polymers in the polymer powder,is preferably such as to provide compliance with the concentrationsstated for auxiliaries for the powder according to the invention.

Ideal properties in the further processing of the powder may be achievedwhen the melting point of the polymer in the first heating procedure isgreater than in the second heating procedure, measured by differentialscanning calorimetry (DSC); and when the enthalpy of fusion of thepolymer in the first heating procedure is at least 50% greater than inthe second heating procedure, measured by differential scanningcalorimetry (DSC). When such conditions are met, the polymer content (ofthe shell or of the coating) of the composite particles has highercrystallinity when compared with other powders which can be produced byprocesses other than co-precipitation of a dissolved polymer withparticles. A particularly suitable material for the laser sinteringprocess is a nylon-12 which has a melting point of from 185 to 189° C.,with preference from 186 to 188° C., an enthalpy of fusion of 112+/−17kJ/mol, with preference from 100 to 125 kJ/mol, and a freezing point offrom 138 to 143° C., preferably from 140 to 142° C.

An embodiment of the invention also includes a process for producing thecomposite particles, which comprises: at least partially dissolving apolymer for the coating in a medium comprising a solvent which at leastpartially dissolves the polymer; adding the inorganic core particles tothe medium, before, during or after at least partially dissolving thepolymer; suspending the core particles in the medium; and thenprecipitating the polymer from the at least partial solution onto thecore particles to obtain the composite particles; wherein the d₅₀ mediandiameter of the core particles is from 1 to 70 μm and the inorganic coreparticle material is at least one selected from the group consisting ofsilicon dioxide, a polyphosphate, a phosphinate, boron carbide, a mixedoxide, a spinel and a ceramic.

In order to produce an at least partial solution, a polymer may bebrought into contact, in the presence of the inorganic core particles,with exposure to pressure and/or heat, with a medium comprising solventwhich dissolves the polymer, and then the polymer is precipitated fromthe at least partial solution, and composite particles according to theinvention are obtained which are produced by core particles coatedentirely or partially with a precipitated polymer. According to theinvention, titanium dioxide is excluded as an inorganic material of thecore particle.

In one preferred process, the thickness of the coating made of theprecipitated polymer may be 1.5 μm or more, preferably 2, 3, 5, 10, 15,20, 25 or 30 μm or more.

In another preferred process, the d₅₀ median diameter of the coreparticles (core of the composite particle) may be from 1 to 60 μm,preferably from 1 to 50 μm, with preference from 1 to 40 μm, morepreferably from 1 to 30 μm, still more preferably from 1 to 25 μm,particularly preferably from 1 to 20 μm and very particularly preferablyfrom 1 to 10 μm. Suitable particle size distributions can be ensured byknown processes, e.g. sieving or sifting.

The use of inorganic core particles which are in suspension in thesolvent for the precipitatable polymer is particularly important. Inthis manner, the inorganic particles provide surface upon which thepolymer precipitates. A feature of one preferred variant of the processof the invention is that a suspension of inorganic core particlessuspended in the alcoholic medium is used, where the (d₅₀) median sizeof the core particles is the size stated above.

The d₅₀ median diameter of the composite particles produced by theproduction process may preferably be from 20 to 150 μm, with preferencefrom 20 to 120 μm, preferably from 20 to 100 μm, more preferably from 25to 80 μm and particularly preferably from 25 to 70 μm.

In the composite particles produced by the production process, the ratioof the d₅₀ median diameter of the composite particles to the d₅₀ mediandiameter of the core particles may preferably be from 1.15 to 30,preferably from 1.2 to 30, with preference from 1.5 to 25; morepreferably from 1.5 to 15, more preferably from 1.5 to 12 andparticularly preferably from 1.5 to 10.

An advantage of the process according to the invention may be providedby, where appropriate, saving an operation during the production of thepowder, because there is no longer any need for the dry-blend mixing ofpolymer particles and auxiliary particles and/or filler particles.

In one preferred process, the core particles are selected from silicondioxide, polyphosphates, phosphinates, boron nitride, boron carbide,mixed oxides, spinels, and ceramic. Particularly preferred coreparticles are of at least one material selected from the groupconsisting of ammonium polyphosphate, silicon dioxide and a phosphinate.

Depending on intended utility and properties, the core particles may besolid beads, hollow beads or porous beads. The shapes of the respectivecore particles may be spherical, lamellar or elongate. The respectivecore particles may optionally, be sharp-edged, rounded-off or smoothparticles. The core particles may optionally be coated with sizes priorto coating via polymer precipitation.

In preferred embodiments of the invention, the precipitatable polymermay be selected from the group consisting of polyolefins, polyethylene,polypropylene, polyvinyl chloride, polyacetal, polystyrene, polyimides,polysulphones, poly(N-methylmethacrylimides) (PMMI), polymethylmethacrylate (PMMA), polyvinylidene fluorides (PVDF), ionomer, polyetherketones, polyaryl ether ketones, polyamide, copolyamide, and mixturesthereof, in particular mixtures of homo- and copolyamide.

In another embodiment, the polymer for coating of the core particles maybe obtained through precipitation of at least one polyamide of AABB typeor through joint precipitation of at least one polyamide of AB type andof at least one polyamide of AABB type. Preference may be given toco-precipitated polyamides, according to this embodiment, where at leastnylon-11 or nylon-12 and at least one polyamide based on PA1010, PA1012,PA1212 or PA1013 are co-precipitated in forming the coating on the coreparticles.

The type of solvent and the content of solvent, and also the otherparameters for dissolving and reprecipitating the appropriate polymer,is dependent on the polymer and is described above.

The following description relates to polymers which can be dissolved inthe alcoholic medium, in particular polyamides. For the coating of coreparticles with polymers for which other solvents must be, or are, used,the parameters and solvents must be modified appropriately, asrecognized by one of ordinary skill in the art.

A feature of a preferred embodiment of the process of the invention isthat a suspension is used which is obtainable by suspending theinorganic core particles in the medium comprising a solvent whichdissolves the polymer, for example an alcoholic medium, withintroduction of energy input greater than 1000 kJ/m³. This generallyalready produces very useful suspensions of the core particles in themedium. The energy input mentioned may be achieved through knownassemblies. Suitable assemblies include, but are not limited to,planetary-gear kneaders, rotor-stator machinery, an agitated ball mill,a roll mill or the like.

The suspensions that are useful for the invention are produced in amedium comprising solvents which dissolve the precipitatable polymer,for example an alcoholic medium. In the case of an alcoholic medium, thesolvent may be a pure alcohol, a mixture of a plurality of alcohols, oralcohols with a content of water or of other substances which do not inessence have any disadvantageous effect on the desired reprecipitationof the polyamides. The alcoholic medium of the suspensions preferablyhas less than 50% by weight content of non-alcoholic substances(preferably water), particularly preferably comprising less than 30% byweight, and particularly advantageously less than 10% by weight, offoreign non-alcoholic substances. The invention may optionally use anyof the types of alcohols or mixtures thereof which permitreprecipitation of polymers, preferably polyamides, under the desiredconditions (pressure and temperature). In any particular case, it isrelatively easy for the person skilled in the art to modify the systemto meet specific requirements. The process of the invention maypreferably use as alcoholic medium for the precipitation of thepolyamide and/or the suspension of the core particles, one or morealcohols which have a numeric ratio of oxygen atoms to carbon atoms inthe range from 1:1 to 1:5.

Suitable alcohols for producing the suspension of the core particles maybe those where the ratio of oxygen to carbon is 1:1, 1:2, 1:3, 1:4 or1:5, preferably those where the ratio of oxygen to carbon is 1:2 or 1:3,particularly preferably where the oxygen to carbon ratio is 1:2. It isvery particularly advantageous to use ethanol for producing a suspensionof the core particles, and also for the reprecipitation of theprecipitatable polymer, preferably of the polyamides.

As previously described, the precipitatable polymer may preferably beselected from the group consisting of polyolefins, polyethylene,polypropylene, polyvinyl chloride, polyacetal, polystyrene, polyimides,polysulphones, poly(N-methylmethacrylimides) (PMMI), polymethylmethacrylate (PMMA), polyvinylidene fluorides (PVDF), ionomer, polyetherketones, polyaryl ether ketones, polyamide, copolyamide and mixturesthereof, in particular mixtures of homo- and copolyamide. Theprecipitatable polyamide is dissolved in an appropriate solvent so thatit can be reprecipitated on the surface of the core particles, therebycoating the particle.

In a highly preferred embodiment, the reprecipitatable polymer may be apolyamide, preferably a polyamide which has at least 8 carbon atoms percarbonamide group. It is particularly preferable that the polymer is apolyamide which has 10 or more carbon atoms per carbonamide group.Polyamides which may preferably be used as starting material for theprocess of the invention comprise inter alia nylon-11, nylon-12 andpolyamides having more than 12 aliphatically bonded carbon atoms percarbonamide group, preferably nylon-12. It is moreover possible to usethe corresponding copolyamides or a mixture of homo- and copolyamideswhere these comprise at least 70 percent by weight of the polymer. Theymay accordingly comprise from 0 to 30 percent by weight of one or morecomonomers, such as caprolactam, hexamethylenediamine,2-methyl-1,5-pentanediamine, 1,8-octamethylenediamine,dodecamethylenediamine, isophoronediamine,trimethylhexamethylenediamine, adipic acid, suberic acid, azeleic acid,sebacic acid, dodecanedioic acid or aminoundecanoic acid. The homo- andcopolyamides, termed polyamides hereinafter, may be used in the form ofgranulated materials or ground material, where the relative solutionviscosity of these is from 1.5 to 2.3 (measured in 0.5% m-cresolsolution at 25° C. in accordance with DIN 53 727), preferably from 1.55to 1.95. They may be produced by polycondensation, or hydrolytic oracidolytic or activated anionic polymerization, by conventionally knownprocesses. In a preferred embodiment, unregulated polyamides withNH₂/COOH end group ratios of from 40/60 to 60/40 may be used. However,it may also be advantageous to use regulated polyamides and specificallypreferably those in which the NH₂/COOH end group ratio is 90:10 and80:20 or 10:90 and 20:80.

Any of methods known to one of skill in the art may be used to producethe solution of the precipitatable polymers, preferably the polyamides,for the reprecipitation process. It may be advantageous to achievemaximum completeness of dissolution of the precipitatable polymers,preferably of the polyamide, in the appropriate medium, preferably analcoholic medium, in the presence of the core particles suspendedtherein. Dissolution may be promoted by use of pressure and/or heat. Inan advantageous procedure, the precipitatable polymer, may initially bepresent in the alcoholic medium and may be dissolved with exposure toelevated temperature for the required time. The suspension of the coreparticles may be added prior to, during or after the dissolution of theprecipitatable polymer. The suspension of the core particles mayadvantageously be present together with the precipitatable polymer, inthe starting mixture. The dissolution procedure may advantageously beassisted by the use of appropriate agitation assemblies. Theprecipitation of the precipitatable polymer may be assisted by usingpressure and/or heat, preferably using a temperature reduction and/orremoval of the solvent, by distillation (preferably under reducedpressure) to precipitate the precipitatable polymer. However, it mayalso be possible to assist the precipitation process by adding ananti-solvent (precipitant).

In an optionally preferred process, after formation of the compositeparticles, a post-treatment may be carried out in a mixer with highshear. The temperature here may particularly preferably be above theglass transition temperature of the respective polymer. This measure mayserve to round the grains and improve powder-flowability.

The abovementioned parameters may be determined as follows:

BET surface area was determined in accordance with DIN ISO 9277: 2003-05with gas-adsorption equipment from Micromeritics for determiningspecific surface area by the BET method (Micromeritics TriStar 3000V6.03: V6.03 refers to the software version of the Win3000 Software).BET surface area was determined by means of nitrogen gas adsorption bythe discontinuous volumetric method (DIN ISO 9277:2003-05, Section6.3.1.). For this, a number (seven) of measurement points weredetermined at relative pressures P/P0 from 0.05 to 0.20. He (purity atleast 4.6 [99.996%] according to operating instructions, or at least 4.0[99.99%] according to standard; this also applies to N₂) was used fordead volume calibration. The samples were devolatilized respectively for1 hour at room temperature (21° C.) and 16 hours at 80° C. in vacuuo.The specific surface area was based on the devolatilized specimen. Theevaluation used multipoint determination (DIN ISO 9277:2003-05, Section7.2). The temperature during the measurement was 77 K.

The particle size (d₅₀ fineness) was determined by means of laserscattering. The measurements were carried out with a Malvern Mastersizer2000. A dry measurement is involved here. For the measurement, in eachcase from 20 to 40 g of powder were metered into the system with the aidof Scirocco dry-dispersion equipment. The feed rate used to operate thevibrating trough was 70%. The pressure of the dispersion air was 3 bar.Each measurement involved a background measurement (10 seconds/10 000individual measurements). The measurement time for the sample was 5seconds (5000 individual measurements). The refractive index, and alsothe blue-light value, was defined as 1.52. Evaluation was based on theMie theory.

Bulk density is calculated in accordance with DIN EN ISO 60.

Particle content is determined by ash/ignition residue determination inaccordance with DIN EN ISO 3451 Part 1 and Part 4.

Solution viscosity was determined in 0.5% meta-cresol solution inaccordance with ISO 307.

In another embodiment, the present invention includes a process forproducing a moulded article, comprising:

applying a layer of the composite powder according to the presentinvention;

selectively melting at least one region of the layer by introduction ofelectromagnetic energy;

allowing the melted region to solidify;

applying another layer of composite powder and repeating the melting andsolidification to perform a layer-by-layer process in which a mouldinghaving a structure according to the selective treatment is obtained;

wherein the melting selectivity is achieved by applying susceptors,inhibitors, or absorbers to each applied layer or by applying a mask tothe applied layer.

Accordingly, regions of the respective powder layer are selectivelymelted through introduction of electromagnetic energy, where theselectivity is achieved by applying susceptors, inhibitors, or absorbersor by masks, where the powder comprises composite particles which areproduced by core particles coated entirely or partially with aprecipitated polymer, where the d₅₀ median diameter of the coreparticles, preferably at least one material selected from the groupconsisting of ammonium polyphosphate, silicon dioxide and a phosphinate,is 1 to 70 μm.

The present invention also provides mouldings obtained from the powderaccording to the invention by the abovementioned process. The mouldingthus produced here comprises (a) polymer(s) preferably selected frompolyolefins, polyethylene, polypropylene, polyvinyl chloride,polyacetal, polystyrene, polyimides, polysulphones,poly(N-methylmethacrylimides) (PMMI), polymethyl methacrylate (PMMA),polyvinylidene fluorides (PVDF), ionomer, polyether ketones, polyarylether ketones, polyamide, copolyamide and mixtures thereof, inparticular mixtures of homo- and copolyamide. In another embodiment, thepolymer may be at least one polyamide of AABB type or a mixture of atleast one polyamide of AB type and of at least one polyamide of AABBtype. Preference is given here to mixtures of polyamides where at leastnylon-11 or nylon-12 and at least one polyamide based on PA1010, PA1012,PA1212 or PA1013 may be present.

The process with use of the powder according to the invention providesadvantages in that the powder no longer demixes, fewer cavities areproduced in the component, and recyclability is better, and thecomponents have higher density and uniform quality, and also in thatthere is clear separation between molten and non-molten regions, and inthat the components have low warpage.

The energy may be introduced through electromagnetic radiation, and theselectivity may be introduced for example, by masks, or application ofinhibitors, absorbers or susceptors, or else by focussing of theradiation, for example by lasers. The electromagnetic radiation maycomprise the range from 100 nm to 10 cm, preferably from 400 nm to 10600 nm or from 800 to 1060 nm. The source of the radiation may be amicrowave generator, a suitable laser, a fibre laser, a radiant heatsource or a lamp, or else a combination thereof. After cooling of all ofthe layers, the moulding can be removed.

The following examples of processes of this type serve for illustration,but there is no intention that the invention be restricted thereto.

Laser sintering processes are based on the selective sintering ofpolymer particles, where layers of polymer particles are briefly exposedto laser light and the polymer particles exposed to the laser light bondto one another. The successive sintering of layers of polymer particlesproduces three-dimensional objects. Details concerning the selectivelaser sintering process may be found in U.S. Pat. No. 6,136,948 and WO96/06881.

Other processes which may be suitability employed include the SIBprocesses described in WO 01/38061, and the process described in EP 1015 214. Both processes operate with large-surface-area infrared heatingfor melting of the powder.

The selectivity of the melting process is achieved in the first case byapplying an inhibitor, and in the second process it is achieved by amask. DE 103 11 438 describes another process in which the energyrequired for the fusion process is introduced through a microwavegenerator, and the selectivity is achieved by applying a susceptor.

Other suitable processes are those operating with an absorber which iseither present in the powder or is applied by ink-jet processes, asdescribed in DE 10 2004 012 682.8, DE 10 2004 012 683.6 and DE 10 2004020 452.7.

A feature of the mouldings according to the present invention which areproduced by a layer-by-layer process in which regions are selectivelymelted is that the density of the moulding component may be reduced incomparison to a component produced from conventionally known powder asdescribed above. Susceptibility to warpage is moreover reduced, and animprovement is achieved in the reproducibility of mechanical propertiesin the moulding.

The mouldings may moreover comprise auxiliaries as described as optionalcomponents for the powder, e.g. heat stabilizers, e.g. stericallyhindered phenol derivatives. The mouldings preferably comprise less than3% by weight of these auxiliaries, based on the entirety of the polymerspresent, particularly preferably from 0.001 to 2% by weight and veryparticularly preferably from 0.05 to 1% by weight.

Application sectors for the said mouldings may be found both in rapidprototyping and in rapid manufacturing. The latter certainly also meanssmall runs, i.e. the production of more than one identical part, wherehowever production by means of an injection mould is not economic.Examples include parts for high specification cars of which only smallnumbers of units are produced, or replacement parts for motorsport,where availability time is important, as well as the small numbers ofunits. Sectors in which the parts are used include but are not limitedto the aerospace industry, medical technology, mechanical engineering,automobile construction, the sports industry, the household goodsindustry, the electrical industry, and the lifestyle sector.

The invention also provides the use of the powder according to theinvention in a process for producing mouldings by a layer-by-layerprocess in which regions of the respective powder layer are selectivelymelted through introduction of electromagnetic energy, where theselectivity is achieved by applying susceptors, inhibitors, or absorbersor by masks, where at least one powder is used which comprises compositeparticles which are coated entirely or partially with a precipitatedpolymer, where the core particles are inorganic core particles, with theexception of titanium dioxide, and where the d₅₀ median diameter of theinorganic core particles is from 1 to 70 μm.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

The values measured for bulk density were determined by an apparatus inaccordance with DIN EN ISO 60.

EXAMPLES Example 1 Reprecipitation of Nylon-12 (PA 12) (not According tothe Invention)

400 kg of unregulated PA 12 produced by hydrolytic polymerization andhaving a relative solution viscosity of 1.62 and 75 mmol/kg of COOH endgroup content and 69 mmol/kg of NH₂ end group content were heated to145° C. with 2500 l of ethanol denatured with 2-butanone and 1% watercontent, within a period of 5 hours in a 3 m³ stirred tank (a=160 cm)and held at the said temperature for 1 hour, with stirring (bladestirrer, x=80 cm, rotation rate=49 rpm). The jacket temperature was thenreduced to 124° C. and the internal temperature was brought to 125° C.at the same stirrer rotation rate with continuous removal of the ethanolby distillation, with a cooling rate of 25 K/h. From this junctureonwards, with the same cooling rate, the jacket temperature was held atfrom 2K to 3 K below the internal temperature. The internal temperaturewas brought to 117° C., with the same cooling rate, and was then heldconstant for 60 minutes. Material was then removed by distillation witha cooling rate of 40 K/h, and the internal temperature was thus broughtto 111° C. At the said temperature, the precipitation process began,discernible from the evolution of heat. The distillation rate wasincreased in such a way that the internal temperature did not risebeyond 111.3° C. After 25 minutes, the internal temperature fell,indicating the end of the precipitation process. The temperature of thesuspension was brought to 45° C. by further removal of material bydistillation and cooling by way of the jacket, and then the suspensionwas transferred to a paddle dryer. The ethanol was removed bydistillation at 70° C./400 mbar, and the residue was then further driedfor 3 hours at 20 mbar/86° C.

This gave a precipitated PA 12 with an average grain diameter of 55 μm.Bulk density was 435 g/l.

By analogy with the procedure indicated in Example 1 or in accordancewith DE 19708146, a powder was produced with particles as core and witha shell made of PA12, PA 10.12, PA10.10, PA6.12, PA6.13, PA10.13, PA6.18and PA12.18.

Example 2 Single-Stage Reprecipitation of PA12 with Particles (Accordingto the Invention)

As in Example 1, 250-375 kg of a PA 12 produced by hydrolyticpolymerization with a relative solution viscosity (η_(rel)) of 1.62 andwith 75 mmol/kg of COOH end group content and 66 mmol/kg of NH₂ endgroup content were reprecipitated in the presence of 162.5-250 kg ofparticles with the properties set out in Table 1:

TABLE 1 Properties of the various core particles used in Example 2:Particle d₅₀ Al₂O₃ (Martoxid ® MN/Y 216) >10 μm Al₂O₃ (Martoxid ® DN206) 5-7 μm Al₂O₃ (Martoxid ® MDLS-6) 3-4 μm Al₂O₃ (Martoxid ® MZS-1)1.5-1.9 μm Ammonium polyphosphate (Exolit ® AP 422) 18.33 μm Phosphinate(Exolit ® OP1230) 11 μm SiO₂ (Aeroperl ® 300/30) 8 μm Stainless steelflakes 31 μm AS081 aluminium powder 28 μm

In this example, the precipitation conditions were altered in thefollowing way in comparison with Example 1:

Precipitation temperature: 108° C.

Precipitation time: 150 min

Stirrer rotation rate: from 39 to 82 rpm

Table 2 collates the characterization (bulk density, diameter and BETsurface area) of the powders produced in accordance with Example 2.Alongside this, Table 2 also gives the amounts used of polyamide, coreparticles and ethanol, and also the stirrer rotation rate used in theprocess.

TABLE 2 Characterization of the powders produced in accordance withExample 2 Core RD SD d₅₀ BET EtOH PA particles rpm g/L μm m²/g L kg kgExolit ® AP 422 in PA12/10.13 77 419 45 6.3 2500 156/156 94 77 425 467.2 2500 156/156 94 Exolit ® AP 422 39 529 66 7.4 2500 348 43 39 388 6111.5 2500 261 87 39 319 56 11.9 2500 243.5 104.5 Exolit ® OP 1230 40 34042.8 10 2500 313 138 40 403 31.8 4.8 2500 313 213 39 135 69 4.1 2500 34835 39 370 61 3.4 2500 348 104 Aeroperl ® 300/30 44 321 54.7 31.6 2500375 44 44 336 49 32 2500 375 44 39 272 42 30.2 2500 348 35 39 296 2658.4 2500 348 105 Martoxid ® MN/Y 216 53 411 67 4.5 2500 375 44 53 42265.2 3.3 2500 375 44 39 371 67 5.1 2500 348 87 39 407 67 5.6 2500 348174 82 340 37 10 2500 348 232 39 423 55 5.7 2500 348 348 Martoxid ® DN206 39 370 56 6 2500 348 174 Martoxid ® MDLS-6 39 388 43 8.1 2500 348174 Martoxid ® MZS-1 39 321 36 10.1 2500 348 174 Stainless steel flakes52 312 74 8.3 2500 348 87 52 297 68 8.4 2500 348 150 52 298 63 8.6 2500348 232 39 327 83 7.3 2500 348 150 65 277 59 10.1 2500 348 150 78 339 667.7 2500 348 39 78 352 68 6.4 2500 348 17.5 Aluminium powder 65 381 574.6 3480 348 87.5 SR = stirrer rotation rate; BD = bulk density

The invention claimed is:
 1. A powder, comprising composite particles:wherein the composite particles, comprise: an inorganic core particlehaving a d₅₀ median diameter of from 1 to 70 μm; and at least a partialcoating of a precipitated polymer on the core; wherein the d₅₀ mediandiameter of the composite particles is from 20 to 150 μm, a ratio of ad₅₀ median diameter of the composite particles to the d₅₀ mediandiameter of the core particles is from 1.15 to 30, a thickness of the atleast partial precipitated polymer coating of the composite particle is1.5 μm or greater, the melting point of the polymer in a first heatingprocedure is greater than in a second heating procedure, as measured bydifferential scanning calorimetry (DSC), the inorganic core particle isat least one material selected from the group consisting of apolyphosphate, a phosphinate, boron carbide and a ceramic, theprecipitated polymer of the coating comprises at least one polymerselected from the group consisting of a polyolefin, a polyethylene, apolypropylene, a polyvinyl chloride, a polyacetal, a polystyrene, apolyimide, a polysulphone, a poly(N-methylmethacrylimide) (PMMI), apolymethyl methacrylate (PMMA), a polyvinylidene fluoride (PVDF), anionomer, a polyether ketone, a poly aryl ether ketone, a polyamide, anda copolyamide, the inorganic core particle material does not includetitanium dioxide, and a melting point of the coating polymer isobtainable when the polymer is exposed to an electromagnetic energy. 2.The powder according to claim 1, wherein the d₅₀ median diameter of thecore particles is from 1 to 60 μm.
 3. The powder according to claim 1,wherein the ratio of the d₅₀ median diameter of the composite particlesto the d₅₀ median diameter of the core particles is from 1.5 to
 15. 4.The powder according to claim 1, wherein a number average weight ratioof the at least partial precipitated polymer coating to the coreparticle, is from 0.1 to
 30. 5. The powder according to claim 1, whereina BET specific surface area of the composite particle is from 1 to 60m²/g.
 6. The powder according to claim 1, wherein the precipitatedpolymer of the at least partial coating is a polyamide having at least 8carbons per carbonamide group.
 7. The powder according to claim 6,wherein the polyamide is at least one selected from the group consistingof nylon-6,12, nylon-11 and nylon-12.
 8. The powder according to claim1, wherein an enthalpy of fusion of the polymer in the first heatingprocedure is at least 50% greater than in the second heating procedure,as measured by differential scanning calorimetry (DSC).
 9. The powderaccording to claim 1, which further comprises at least one selected fromthe group consisting of a powder flow-aid, a pigment and a heatstabilizer.
 10. The powder according to claim 9, wherein a content ofthe composite particles in the powder is at least 50% by weight.
 11. Aprocess for producing the composite particles according to claim 1, theprocess comprising: at least partially dissolving a polymer for thecoating in a medium comprising a solvent which at least partiallydissolves the polymer; adding the inorganic core particles to themedium, before, during or after at least partially dissolving thepolymer; suspending the core particles in the medium; and thenprecipitating the polymer from the at least partial solution onto thecore particles to obtain the composite particles; wherein the d₅₀ mediandiameter of the core particles is from 1 to 70 μm.
 12. The processaccording to claim 11, wherein a density of the core particles isgreater or not more than 20% smaller than the density of the solventused for the precipitation of the polymer.
 13. The process according toclaim 11, wherein the solvent for the polymer is ethanol and a densityof the core particles is greater or not more than 20% smaller than thedensity of ethanol.
 14. A process for producing a moulded article, theprocess comprising: applying a layer of the composite powder accordingto claim 1; selectively melting at least one region of the layer byintroduction of electromagnetic energy; allowing the melted region tosolidify; applying another layer of composite powder and repeating themelting and solidification to perform a layer-by-layer process in whicha molding having a structure according to the selective treatment isobtained; wherein the melting selectivity is achieved by applyingsusceptors, inhibitors, or absorbers to each applied layer or byapplying a mask to the applied layer.
 15. A moulded article obtainedaccording to the process of claim 14.